In recent years, secondary batteries have been increasingly used. In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, meanwhile, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, which exhibit high energy density, discharge voltage, and output stability, is very high.
In addition, secondary batteries may be classified based on the structure of an electrode assembly having a positive electrode/separator/negative electrode structure. For example, the electrode assembly may be configured to have a jelly-roll (wound) type structure in which a long sheet type positive electrode and a long sheet type negative electrode are wound in the state in which a separator is disposed between the positive electrode and the negative electrode, a stacked type structure in which pluralities of positive electrodes and negative electrodes each having a predetermined size are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes, or a stacked/folded type structure in which predetermined numbers of positive electrodes and negative electrodes are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes to constitute a bi-cell or a full cell, and then a plurality of bi-cells or full cells is folded using a separation film.
In recent years, much interest has been taken in a pouch-shaped battery configured to have a structure in which such a stacked or stacked/folded type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, easy modification in shape, etc. In addition, the use of such a pouch-shaped battery has gradually increased.
FIGS. 1 and 2 are exploded perspective views typically showing a general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1, a pouch-shaped secondary battery 10 includes a stacked type electrode assembly 20 having pluralities of electrode tabs 21 and 22 protruding therefrom, two electrode leads 30 and 31 respectively connected to the electrode tabs 21 and 22, and a battery case 40, in which the stacked type electrode assembly 20 is received in a sealed state such that the electrode leads 30 and 31 are partially exposed outward from the battery case 40.
The battery case 40 includes a lower case 42 having a depressed receiving part 41, in which the stacked type electrode assembly 20 is located, and an upper case 43 for covering the lower case 42 such that the electrode assembly 20 is sealed in the battery case 40. The upper case 43 and the lower case 42 are connected to each other by thermal welding in the state in which the stacked type electrode assembly 20 is mounted therein to form an upper end sealed part 44, side sealed parts 45 and 46, and a lower end sealed part 47.
As shown in FIG. 1, the upper case 43 and the lower case 42 may be configured as separate members. As shown in FIG. 2, on the other hand, one end of the upper case 43 may be integrally formed at a corresponding end of the lower case 42 such that the upper case 43 and the lower case 42 may be hingedly connected to each other.
In addition, as shown in FIGS. 1 and 2, the pouch-shaped battery cell is configured to have a structure in which electrode terminals constituted by the electrode tabs and the electrode leads connected to the electrode tabs are formed at one end of the electrode assembly. Alternatively, a pouch-shaped battery cell configured to have a structure in which electrode terminals are formed at one end and the other end of an electrode assembly may also be manufactured using the above-described method.
Meanwhile, FIGS. 1 and 2 show the pouch-shaped battery cell having the stacked type electrode assembly. Alternatively, a pouch-shaped battery cell having a wound type or jelly-roll type electrode assembly may also be manufactured using the above-described method.
As shown in FIGS. 1 and 2, the pouch-shaped battery cell is generally configured to have an approximately rectangular hexahedral shape.
However, devices, to which the pouch-shaped battery cell is applied, may be configured to have various shapes other than a rectangular hexahedral shape. The devices may even be configured to have a curved shape. For example, the sides of a smart phone may be curved so as to be easier to grip, and a flexible display device may be curved or bent. That is, the flexible display device may be manufactured to have various shapes.
In the case in which a battery cell or battery pack configured to have a rectangular hexahedral shape is mounted in a device designed so as to have such curved parts or a device that can be curved, however, the efficiency of utilization of the space in the device may be lowered. In recent years, it has been required for the battery cell to be flexible such that the battery cell can be easily mounted in devices configured to have various kinds of designs.
In a device designed so as to have such curved parts or a deformable device that can be curved or bent, however, a cell case may be damaged when a battery cell received in the device is deformed, with the result that a metal layer may be exposed from the cell case or an electrolyte may leak from the cell case.
Therefore, there is a high necessity for technology that is capable of ensuring the safety of a battery even when the battery is deformed while solving the above problems.